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Variations in the polymer/monomer mixing ratios from 1.5:1 to 4.5:1 vol/vol have been evaluated to determine the effect on dimensional accuracy and impact resistance of a PMMA homopolymer. Two polymerisation cycles were used. It was shown that a wide variation in mixing ratios (1.5:1 to 4:1) had no effect on dimensional accuracy or impact resistance and that a polymerisation cycle that includes a final boiling period is preferred. It was further found that notched impact resistance was almost an order of magnitude below unnotched impact resistance, emphasising the weakening effect of sharp contours on the impact resistance of denture resins.

Trevalon is a denture base material which can be cured by three basic alternative curing cycles, thus providing a choice of processing technique which can be selected to suit laboratory or clinical needs. The flexibility of working properties is probably due to the interaction between on the one hand, the high molecular weight of the powder and on the other hand, the particle size distribution which are important factors influencing the doughing time (14 min), working time (40 min) and the exothermic reaction. The effect of each curing cycle upon the following properties of the material was investigated; dimensional accuracy, Young's modulus, modulus of rupture, impact resistance, water sorption, indentation resistance, creep and transverse bend behaviour. The particle size and molecular weight distribution of the powder were also evaluated. A clinical investigation of Trevalon was carried out by constructing complete dentures for a sample of patients, divided into three groups, each group having dentures processed by one of the three alternative curing cycles. Although some laboratory tests demonstrated that there were statistically significant differences between specimen bases, no clinical differences were recorded between dentures 1 year after construction.

The applicability of an electronic thermometer CRAFTEMP in taking intraoral temperatures was determined. Sublingal temperatures in ten young subjects with complete natural dentitions, and the temperatures at the denture base-mucosa interface and on the polished surface of both maxillary and mandibular complete dentures in ten elderly patients were measured. The results showed that there was a temperature difference between the polished surface of the maxillary denture and the denture base-mucosa interface. This was statistically significant in the female but not in the male subjects. No temperature difference could be demonstrated with any of the mandibular dentures. The CRAFTEMP was found to be a convenient and reliable method for intraoral temperature measurement.

Differential scanning calorimetry has been used with success to determine working and setting times of autopolymerizing denture and orthodontic base resins. The technique is considered to be far more suitable for this task than thermal methods which are influenced by specimen geometry and heat transfer. Since only a few milligrams of material are required the technique would be suitable for other dental materials whose setting characteristics are of interest.

Interactive video is computer-aided learning illustrated by still or moving video pictures. First introduced for the study of pathology, its application and potential in prosthodontics is reported in this article. Partial denture design was chosen as the first subject, since the systematic approach concept could easily be established by dividing the subject into five units that could individually be expanded and tested. Students are generally enthusiastic about computer-aided learning and there is considerable potential to further develop this type of learning process.

A method of measuring creep, recovery, hardness, and the effect of cyclic loading on denture base polymers using a modified Wallace hardness tester is described. This apparatus is particularly sensitive and is capable of detecting very small variations in these properties of the materials. A representative group of denture base polymers that include heat-cured, pour-type, and other modified materials was tested. The results obtained are in good agreement with those shown by other workers.

Concentrations of chlorinated hydrocarbons in airborne dust carried by the trade winds from the European-African land areas to Barbados range from less than 1 to 164 parts per billion. The lower limit of the average content of 1 cubic meter of air is 7.8 x 10-(14) gram. The contributions of river-borne and atmospherically transported pesticides to parts of the marine environment are calculated approximately and comtpared. The amnounts of pesticides contributed to the tropical Atlantic by the trade winds appear to be comparable to those carried to the sea by major river systems.